Atomizing magnesium and its alloys



April 27, 1954 D. s. CHISHOLM 2,675,359

ATOMIZING MAGNESIUM AND ms ALLOYS Filed May 15, 1950 INVEN TOR. Doug/055 Ch/s/w/m A TTORNE Y5 Patented Apr. 1954 UNITED sTA Es v PATENT OFFICE,ac'zasso y.

as. M Application May 15, 1950, Serial N0. 161,972

The invention relates to a method of atomizing magnesium and its alloys.

In my copending application Serial No. 159,370, filed May 1, 1950, thereis disclosed a method of atomizing magnesium and its alloys whichinyolves the impingement of a cool hydrocarbon gas (methane, ethane,propane, butane) againstathin stream of the molten metal. The cool Basbreaks up the molten metal into fine spherical droplets which solidifyinto smooth spheres with an invisible protective coating. The coatedparticles thus obtained are unique in that, among other unusualproperties they possess, they do not become united into a compact evenunder the application of compressive pressures as high as 100,000 poundsper square inch,.and they are diillcult to ignite with the flame of amatch.

The present invention concerns a modification of the foregoing method ofatomizing magnesium and its alloys and is based upon the discovery thatby mixing with the hydrocarbon gas used to atomize the molten metal asufllcient quantity of a fog-forming liquid to at least saturate theatomizing gas with the vapor of the liquid and entrain some of theliquid in the atomizing gas as a fog, the solid atomized particles ofmetal obtained are jagged rather-than smooth, are capable of beingcompacted under pressure, and readily ignite with the flame of a match.The invention then consists of the method hereinafter fully describedand particularly pointed out-in the claims, reference being had to theaccompanying drawing.

In the said drawing. Fig. 1 is a photograph at a magnification of 7diameters of a sample of atomized magnesium alloy made by atomizing withdry hydrocarbon gas, the sample, being a Claims. (CI- 18-47.

spread thinly on a flat white background. Fig. 2

is a similar photograph of a thinly spread sample of the samemagnesium-base alloy atomized according to the method of the inventionusing water saturated natural gas containing entrained liquid water as afog.

In carrying out the invention, the magnesium or magnesium-base alloy tobe atomized is brought to the molten state and heated preferably notmore than about 100 to 250 Fahrenheit degrees above the melting point.The molten metal is allowed to fall in a thin stream and a jet ofhydrocarbon gas of the paraflln series at least saturated withfog-forming liquid is impinged against it. The size of the metal streamdoes not appear to be critical. Where very. high rates of production arenot required, a stream of diameter 2 velocity of the hydrocarbon gas doenot appear to be sharply critical and satisfactory atomizing can be hadwithgas pressures at the jet as low as 15 pounds per square inch and ashigh as pounds per square inch or more. The diameter of the gas jet ispreferably greater than that of the stream of metal.

The hydrocarbon gases which may be used contain from 1 to 4 carbonatoms, e. g. methane, ethane, propane, and butane. Mixtures of thesegases may be used. They may be saturated with the fog-forming liquid inany convenient manner as by introducing the liquid into the gas as itflows to the jet. The amount of fog-forming liquid beyond that needed tosaturate the atomizing gas is not sharply critical. An excess, beyondsaturating amounts, of about 0.05 gram per cubic foot of the ga measuredat atmospheric pressur is sufllcient. although larger amounts giay beused. For example, at F. about 0.5 gram of water per cubic foot of thegas before compressing to jet pressure is sufilcient to produce about 2per cent by weight more water in the gas than is needed for saturationand produces a fog as the compressed gas issues from the jet. No harmappears to result from the use of a considerable quantity of thefog-forming liquid, 1. e. far more than is needed to saturate the gaswith the vapor of the liquid. An excess, over saturating amounts, of upto about 5 grams per cubic foot is tolerable. Over-saturating theatomizing gas withthe fogforming liquid to produce a fog therein isreadily accomplished byv spraying the fog-forming liquid into'the gasstream on its way to the atomizingv jet so-that a or fog is formed inthe gas jet stream before it strikes the molten metal to be atomized. I,

While water is the preferred fog-forming liquid, other liquids may beused having; a boiling point betweenabout 50 C. and C. Examples ofliquids boiling within the aforesaid range are octane, isobutyl alcohol,ethyl alcohol. methanol. propyl alcohol, toluene, benzene, xylene, andlight distillate. These liquids are generally neutral, 1. e. neitheracid nor alkaline and do not actively attack the magnesium. ey add tothe cooling eiIect of the atomizing g by abstracting heat from themolten metal as the liquid particles of the fog evaporate.

Referring to Fig. 2, as an example of the product of the invention, itwill be seen that the atomized particles are characterized by jaggednessof shape, the surface is rough and is comprised of many sharp points andsharp edges.

of 0.08 to 0.25 inch is generally satisfactory. The 55 These particlesresulted from aomizing a mag- 3 nesium-base alloy having a nominalcomposition 01' 3 per cent of aluminum, 1 per cent or zinc,

0.5 per cent of manganese, the balance being magnesium. In the atomizingoperation, the alloywas melted and heated to 1300 1". A Jet oi wetnatural gas having a diameter of 0.25 inch was impinged upon stallingstream of the heated alloy having a diameter of 0.1 inch at the point ofapplication the gas jet. The atomizing gas, before the addition 0! thewater, contained by volume per cent N3, 80 per cent CH4. 8 per centCalls, and 2 per cent Cal-Is. To this atomizing gas was added about 0.5gram of liquid water per cubic foot or .the atomizing gas at roomtemperature which was then compressed to pounds per square inch andimpinged by means or a Jet against the falling molten metal stream.

For comparison, the same alloy atomized in the same manner with the samehydrocarbon gas before the addition of water produced smooth sphericalparticles, as shown in Fig. 1.

y The jagged particles obtained according to the invention, unlike thoseobtained with dry natural gas atomization, are compactable, nonireeflowing, and can be ignited with the flame oia match. They are moresuitable for pyrotechnical purposes than the rounded particles.

I claim:

l. The method of convertinga molten mass 4 consisting of magnesium oralloy thereof into solid particles having a Jagged form which consistsin letting fall the molten mass in a thin stream and directing a Jetconsisting of parailln hydrocarbon gas against the fallin stream withsuillcient velocity to break up the stream into particles, thehydrocarbon gas being selected from the group consisting of methane,ethane, propane, and butane and containing an entrained neutral liquidas a fog in amount between about 0.05 and 5 grams per cubic foot ofthegas beyond that required for saturation at atmospheric pressure, saidentrained neutral liquid having a boilin; point between and C.

2. The method according to claim 1 in which the entrained neutral liquidis water.

References Cited in the ills of this patent UNITED s'ra'rns PATENTSNumber Name Date 1,351,865 Nicol Sept. 7, 1020 2,371,105 Lepsoe Mar. 6,1045 2,436,520 Mahoney et ai. Feb. 24, 1948 OTHER REFERENCES .Ber. No.268,381, Kaui'mann (A. P. 0.) published July 13, 1943. a

1. THE METHOD OF CONVERTING A MOLTEN MASS CONSISTING OF MAGNESIUM OFALLOY THEREOF INTO SOLID PARTICLES HAVING A JAGGED FORM WHICH CONSISTSIN LETTING FALL THE MOLTEN MASS IN A THIN STREAM AND DIRECTING A JETCONSISTING OF PARAFFIN HYDROCARBON GAS AGAINST THE FALLING STREAM WITHSUFFICIENT VELOCITY TO BREAK UP THE STREAM INTO PARTICLES, THEHYDROCARBON GAS BEING SELECTED FROM THE GROUP CONSISTING OF METHANE,ETHANE, PROPANE, AND BUTANE AND CONTAINING AN ENTRAINED NEUTRAL LIQUIDAS A FOG IN AMOUNT BETWEEN ABOUT 0.05 AND 5 GRAMS PER CUBIC FOOT OF THEGAS BEYOND THAT REQUIRED FOR SATURATION AT A ATMOSPHERIC PRESSURE, SAIDENTRAINED NEUTRAL LIQUID HAVING A BOILING POING BETWEEN 50* AND 175* C.